November 2002 Cainozoic Research, 1(1-2X2001), pp. 3-12, The mesogastropod Littorina littorea (Linné, 1758) in Iceland: palaeobiogeography and migration Ólöf+E. Leifsdóttir & Leifur+A. Símonarson University ofIceland, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland; e-mail: [email protected], and [email protected] Received 5 April 2001; revised version accepted 29 September 2001 in Atpresent, the periwinkle, Littorina littorea (Linné, 1758), is not found living Iceland. The only confirmedoccurrence of the species in Icelandic sediments is in the Middle Pleistocene upper littoral conglomerate at Búlandshöfdi, Snaefellsnes, West Iceland. These layers were deposited during an interglacial stage, slightly older than 1.1 Ma. The species apparently evolved from the Pacific L. squalida Bro- & derip Sowerby, 1829, after the trans-Arctic/North Atlantic migration from the Pacific, possibly in response to cooling and increasing 2.55 environmental energy. The oldest fossil occurrence of L. littorea is in the British Red Crag Formation, between and 2.4 Ma; it is unknown from the Pliocene Tjörnes deposits in N Iceland, older than 2.6 Ma. This indicates that the species separation postdates the deposition of the uppermost Serripes Zone of Tjörnes, after the tide of the migration wave passed Iceland, but before it reached the The taxonomic and of North Atlantic molluscs North Sea area and Britain, between 2.6 and 2.4 Ma. diversity palaeobiogeography were about greatly affected by the major climatic changes that resulted in an extensive glaciation at 2.5 Ma. Key words: Mesogastropoda,Littorina, Iceland, MiddlePleistocene, speciation, palaeobiogeography, migration. Introduction Growth lines are distinctly prosocline and form an angle of about 120° with the axis of the spire. Spiral ridges and The prosobranch mesogastropod Littorina littorea was grooves are slight and numerous, and especially marked in described Linne who named it Turbo but tend to become obscure in older originally by (1758), young individuals, established the The ribs low and The littoreus. In 1822, Ferussac genusLittorina, ones. numerous are very narrow. T. littoreus being its type species now. Since the times of aperture is oval and angulate in the uppermost part and lies these workers, there have been a number of incorrect in a prosocline plane with the peristome. The outer lip spelling and minor nomenclatorialcomplications, but these meets the periphery of the body at an angle of 125-130° to will not be enumerated here. Several doubtful records of the axis. The inner lip is thick and lacks an umbilical fossil exist in Iceland. The aim of the The white columella is short and inclined towards living and Littorina groove. of shell’s axis. Colours of the shell from present study is to attempt to clear up the occurrence L. the vary cream to littorea in Iceland and to provide a more precise picture of brown, black, brownish black, grey, orange or red, but the palaeobiogeography of the species. usually the shell is pale brown with 8-25 narrow black to The material studied comprises specimens collected by dark brown lines. The body whorl is around80-85% ofthe in and total ofthe shelland the ofthe is 60- the authors, as well as specimens kept geological height height aperture littorea zoological museums in Iceland and Denmark. 70%. The adult shell of L. is the largest of the ge- nus with a mature shell height between 10.6 and 52.8 mm Abbreviationsused in the text are as follows: (Reid, 1996). The protoconch consists of two or more unsculpted whorls (Fretter & Graham, 1980). The snout is IMNH Icelandic Museum of Natural History, Reyk- broad, slightly tapered and distally truncated. The terminal mouth is ventral the head and has radula with javik. slightly on a NHM The Natural History Museum, London. a relative length from 1.49 to 2.15 mm (Reid, 1996). The cephalic tentacles each have an eye on a lateral bulge at the base. The foot is elongated and shield-shaped. The oper- culum has 2-3 and nucleus the colu- Diagnosis turns a displaced to mellar side. There is a linear osphradium and a long gill in the mantle to the left. The with 10-42 mamil- The typical adult shellof L. littorea is solid with a pointed, cavity penis, liform is and cyrtoconoid spire and 5-6 whorls, which are slightly tumid glands, sickle-shaped tapers abruptly distally. Vermeij (1982) found some patterns in shell thickness to nearly flat in profile (Figure la, b). The upper part ofthe scale. the on a geographical body whorl is straight to concave, especially near ap- erture. The suture is shallow, resulting in a flat perimeter. -4- Figure 1. Species ofLittorina. a L. littorea(IMNH 754), Recent specimenfrom Rorvig, Denmark; b L. littorea (IMNH 755), from Middle Holocene Stone Age sea deposits in Denmark; c,d L. littorea (IMNH 756), from MiddlePleistocene interglacial deposits at Bulandshofdi (W Iceland); e,f L squalida (IMNH 3976), from horizon 11 ofthe Pliocene Mactra Zone ofthe Tjomes beds, N Iceland (afterReid, 1996); g,h L. islandica (IMNH 3977, paratype), from horizon 25 of the Pliocene Serripes Zone of the Tjomes beds, N Iceland (after Reid, 1966). In North America, the shells become thinner to the south of population has recently been discovered at Castiglioncello, Cape Cod, which indicates a relationship between tem- NW Italy (Barsotti & Campani, 1982). perature, growth rate and shell form. In brackish habitats, In the western Atlantic, L. littorea is distributed from shells are both smaller and thinner with a fainter texture, the Strait of Belle Isle (Newfoundland) in the north to Vir- and the spire height seems to increase with decreasing ginia in the south. The coast of Connecticut is the most salinity (Reid, 1996). southerly suitable habitat, but occasionally currents trans- south far mid-New and the port larvae as as Jersey Del- Recent distribution marva Peninsula where settlement sometimes occurs (Reid, 1996). According to Vermeij (1982), the southernmost Littorina littorea is widely distributed on European shores occurrence seems to have been at Wachapreague in Vir- (Figure 2) from the White Sea in the north to southern ginia. Portugal in the south (Fretter & Graham, 1980; Reid, In the East Pacific, the species has been recorded from 1996). The most northerly record from southern Svalbard the Puget Sound (Washington), San Francisco Bay and confirmed. The Trinidad these the has (Rozycki, 1991) has not yet been species Bay (California). In places, species Bornholm. Further south it able The extends into the Baltic as far as not been to establish populations (Reid, 1996). is common along the French Atlantic coast as far as lie vertical range is from 0 m at several localities, to a depth of d’Oloron. The southern limit in the eastern Atlantic is about 60 m in northern Britain and Skagerrak (Fretter & close to Algarve in southern Portugal. There are some Graham, 1962, 1980; Reid, 1996). The species prefers the doubtful records from the Mediterranean, but a breeding intertidalzone. -5 - of been Figure 2. Recent distribution Littorina littorea. Triangles mark either unverified finds or occurrences where the species has not able to produce established populations. The regional division of northern European seas is based on Feyling-Hanssen (1955), as modifiedby Simonarson et al. (1998). littorea recorded from found Littorina was Greenland by ‘Some few specimens not more than 15 mm long are Fabricius (1780), but that was a misidentification of L. in the Museum of Christian VIII labelled "ex Islandia, saxatilis (Olivi, 1792). Another Greenland record was Johnsen", but it seems probable to me that a confusion has based on incorrectly localised material (Reid, 1996). The taken place’. These four specimens are still in the Zoologi- species was recorded three times from the Faroe Islands in cal Museum (Copenhagen). They are all without animals the 19th century, but it has not been found again despite and so fresh looking that they are probably not of subfossil further collectionefforts (Morch, 1868; Sparck & Thorson, origin (Thorson, 1941). Furthermore, one shell is labelled 1933). Tsld Steenstrup’ and Thorson (1941, p. 34) came to the Turbo first mentioned ‘ subfossiT. The collection From Iceland, littoreus was by conclusion, that it could be Mohr (1786). However, it is quite clear from his descrip- also contains two more shells from Iceland labelledLitto- tion that he was actually dealing with L. obtusata (Linne, rina littorea. One was found in the tidal zone of Isafjordur 1758) and L. saxatilis, without separating them. Then (NW Iceland) and the other among stones on the shore in Morch (1868, p. 207) stated (in Danish, here translated), Amarfjordur (also NW Iceland). These shells are in the -6- and 6-7 weeks & The animal Zoological Museum (Copenhagen), our re- even (Fretter Graham, 1980). to saxatilis. reach of 20 examinationhas revealedthey all belong L. may an age nearly years (Woodward, 1913). Furthermore, it looks like some mixup took place when the shells from Isafjordur and Amarfjordur were labelled at the museum, as Johansen (1901), who found them, re- Fossil occurrence ferred to them as L. groenlandica Menke, 1830 and L. rudis (Maton, 1797). Finally, it should be mentionedthat The stratigraphical range of L littorea is apparently from found in old Danish that the Pliocene the For the Plio-Pleistocene shells of L. littorea were an ship to present day. Iceland. The the between the Reuverian and stranded on Flatey in Breidafjordur, West boundary we use boundary the of The the shells probably came with ballast in the ship from Den- Praetiglian stages Netherlands, at beginning of the first in the Northern mark (Oskarsson, 1973). These are the only known records major glaciation Hemisphere, in and of L. littorea from Iceland, and since no living specimens since this is commonly used northern western have been collected from Icelandic waters it probably does Europe (Zagwijn, 1992; Morrison & Kukla, 1998; Simonarson The of this is close not live there at present.